Question

操作符用来连接运算元。

Expression = UnaryExpr | Expression binary_op Expression .
UnaryExpr  = PrimaryExpr | unary_op UnaryExpr .

binary_op  = "||" | "&&" | rel_op | add_op | mul_op .
rel_op     = "==" | "!=" | "<" | "<=" | ">" | ">=" .
add_op     = "+" | "-" | "|" | "^" .
mul_op     = "*" | "/" | "%" | "<<" | ">>" | "&" | "&^" .

unary_op   = "+" | "-" | "!" | "^" | "*" | "&" | "<-" .

比较运算符在此处讨论。对于其他二元操作符，两个操作元的类型必须是相同的，除了位移和无类型常量。针对常量的操作，请看常量表达式章节。

除了位移操作，如果其中一个操作符是无类型常量，而另个不是，那么无类型的常量会转换成另一个运算元的类型。

在右移表达式中的运算元必须是无符号的整数或者可以转换成 uint 的无类型的常量。如果左移一个无类型常量那么结果依然是无类型的。他首先会转换成指定类型。

var s uint = 33
var i = 1<<s           // 1 has type int
var j int32 = 1<<s     // 1 has type int32; j == 0
var k = uint64(1<<s)   // 1 has type uint64; k == 1<<33
var m int = 1.0<<s     // 1.0 has type int; m == 0 if ints are 32bits in size
var n = 1.0<<s == j    // 1.0 has type int32; n == true
var o = 1<<s == 2<<s   // 1 and 2 have type int; o == true if ints are 32bits in size
var p = 1<<s == 1<<33  // illegal if ints are 32bits in size: 1 has type int, but 1<<33 overflows int
var u = 1.0<<s         // illegal: 1.0 has type float64, cannot shift
var u1 = 1.0<<s != 0   // illegal: 1.0 has type float64, cannot shift
var u2 = 1<<s != 1.0   // illegal: 1 has type float64, cannot shift
var v float32 = 1<<s   // illegal: 1 has type float32, cannot shift
var w int64 = 1.0<<33  // 1.0<<33 is a constant shift expression